1. Field of the Invention
The present invention relates to an organic electro-luminescence device, and more particularly, to an organic electro-luminescence device having upper and lower substrates asymmetrically attached to each other and a method fabricating method same.
2. Description of the Related Art
In the field of flat panel display devices, liquid crystal display devices (LCD) are widely used because of they are lightweight and have low power consumption. However, the LCD is a non-luminous display device and has technical limitations with regard to brightness, contrast, viewing angle, and large display size. Therefore, new flat panel display devices capable of overcoming these drawbacks are actively being developed.
One of these new flat panel display devices is the organic electro-luminescence display device. The organic electro-luminescence devices are self-luminous display devices, therefore they have high contrast and a wide viewing angle compared with LCDs. Also, since the organic electro-luminescence device does not require a backlight assembly, it is lightweight and slim. In addition, the organic electro-luminescence device can decrease power consumption.
Further, the organic electro-luminescence device can be driven with a low DC voltage and has a fast response speed. Since all of the components of the organic electro-luminescence device are formed of solid materials, it is durable against external impact. It can also be used in a wide temperature range and can be manufacture at a low cost.
Specifically, the organic electro-luminescence device is easily fabricated through a deposition and encapsulation process. Therefore, the apparatus and method of fabricating the organic electro-luminescence device are simpler than those of an LCD or PDP.
If the organic electro-luminescence device is driven in an active matrix type, uniform brightness can be obtained even when a low current is applied. Accordingly, the organic electro-luminescence device has the advantages of low power consumption, high definition and large-sized screen.
FIG. 1 is a schematic view of a section of a related art active matrix organic electro-luminescence device (AMOLED) that operates in a bottom emission type.
As illustrated in FIG. 1, first and second substrates 10 and 30 are arranged to face each other. Edge portions of the first and second substrates 10 and 30 are encapsulated by a seal pattern 40. A TFT (T) is formed on a transparent substrate 1 of the first substrate 10 in each sub-pixel unit. A first electrode 12 is connected to the TFT. An organic electro-luminescence layer 14 is formed on the TFT and the first electrode 12 and is arranged corresponding to the first electrode 12. The organic electro-luminescence layer 14 contains light emission materials taking on red, green and blue colors. A second electrode 16 is formed on the organic electro-luminescence layer 14.
The first and second electrodes 12 and 16 function to apply an electric field to the organic electro-luminescence layer 14.
Due to the seal pattern 40, the second electrode 16 and the second substrate 30 are spaced apart from each other by a predetermined distance. Therefore, an absorbent (not shown) and a translucent tape (not shown) may be further provided on an inner surface of the second substrate 30. The absorbent absorbs moisture introduced from the exterior, and the translucent tape adheres the absorbent to the second substrate 30.
In the bottom emission type structure, when the first electrode 12 and the second electrode 16 are respectively an anode and a cathode, the first electrode 12 is formed of a transparent conductive material and the second electrode 16 is formed of a metal having a low work function. In such a condition, the organic electro-luminescence layer 14 includes a hole injection layer 14a, a hole transporting layer 14b, an emission layer 14c, and an electron transporting layer 14d, which are sequentially formed on a layer contacting with the first electrode 12.
The emission layer 14c has red, green and blue color filters in sub-pixels.
Like this, in the related art organic electro-luminescence device, the array element (A) and the organic electro-luminescence diode (E) are stacked on the same substrate.
The bottom emission type organic electro-luminescence device is fabricated by attaching the substrate, where the array element and the organic electro-luminescence diode are formed, to the separate substrate provided for the encapsulation. In this case, the yield of the organic electro-luminescence device is determined by the product of the yield of the array element and the yield of the organic electro-luminescence diode. Therefore, the entire process yield is greatly restricted by the late process, that is, the process of forming the organic electro-luminescence diode. For example, even though excellent array elements are formed, if foreign particles or other factors cause defects in forming the organic electro-luminescence layer using a thin film of about 1000 Å thick, the corresponding organic electro-luminescence device is a defective grade.
Thus, there occurs loss of every expense and material cost spent in fabricating the non-defective array element, resulting in yield reduction.
In addition, the bottom emission type organic electro-luminescence device has high stability and high degree of freedom due to the encapsulation, but has limitation in aperture ratio. Thus, the bottom emission type organic electro-luminescence device is difficult to apply to high-definition products. Meanwhile, in the case of the top emission type organic electro-luminescence device, the design of the TFT is easy and the aperture ratio is high. Thus, it is advantageous in view of lifetime of the product. However, since the cathode is disposed on the organic electro-luminescence layer, the selection of material is restricted. Consequently, the transmittance is limited and the luminous efficiency is degraded.